Ch. 3 Flashcards

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1
Q

What is the measure of disorder in a system called?

A

Entropy

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2
Q

Which of the following represents energy in its most disordered form?

A

Heat energy

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3
Q

Because they generate order (by surviving, growing and forming complex communities), living cells defy the second law of thermodynamics.

A

False

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4
Q

Which of the following does NOT follow the first law of thermodynamics?

A

The use of heat to burn foodstuff inside cells

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5
Q

What is the origin of the energy that animals acquire by eating plants or other animals?

A

Sunlight

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6
Q

Which energy conversion characterizes photosynthesis?

A

Electromagnetic (light) energy → chemical bond energy

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7
Q

In both plants and animals, the process of “controlled burning” that extracts energy from food molecules is a process of gradual:

A

oxidation.

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8
Q

Which of the following does not describe oxidation?

A

The conversion of a chlorine atom to Cl-

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9
Q

Which of the following does describe oxidation?

A

The addition of oxygen atoms to a molecule and The removal of electrons from a molecule

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10
Q

Which of the following statements is NOT true?

A

Hydrogenation reactions are oxidations, and dehydrogenation reactions are reductions.

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11
Q

Which of the following statements IS true?

A
  • Oxidation and reduction reactions always occur simultaneously.
  • When a sugar molecule is oxidized to CO2 and H2O, O2 molecules are reduced.
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12
Q

Chemical reactions proceed spontaneously only in the direction that:

A

leads to a loss of free energy.

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13
Q

In thermodynamics, what does the term “free energy” refer to?

A

Energy that can be harnessed to do work or drive chemical reactions

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14
Q

Which statement about enzymes is NOT true?

A

Enzymes can force reactions to occur that are overall energetically unfavorable.

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15
Q

Which statement about enzymes IS true?

A
  • Enzymes can speed up energetically favorable reactions.

- Enzymes can help build highly ordered structures.

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16
Q

What is the term for the extra energy boost required to initiate an energetically favorable reaction?

A

Activation energy

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17
Q

An enzyme can lower the activation energy of a reaction.

A

TRUE

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18
Q

.After an enzyme catalyzes a reaction, the enzyme has been consumed and cannot perform additional reactions.

A

FALSE

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19
Q

A reaction occurs spontaneously only if the change in free energy (/δ∊λταG) is:

A

negative.

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20
Q

Energetically favorable reactions are those that create disorder by decreasing the free energy of the system to which they belong.

A

True

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21
Q

Which of the following results in increased disorder?

A

Dissolving salt in water

22
Q

nergetically unfavorable reactions can occur if they are coupled to a second reaction with a negative /δ∊λτα Gso large that the net /δ∊λτα Gof the entire process is negative.

A

True

23
Q

Which is NOT true of a reaction at chemical equilibrium?

A

Both the forward and reverse reactions have completely stopped.

24
Q

Which IS true of a reaction at chemical equilibrium?

A
  • /delta G is equal to zero.

- The rates of the forward and reverse reactions are equal.

25
Q

The free energy change (/δ∊λτα G) and the standard-free energy change(/δ∊λτα G°) of a reaction differ in that /δ∊λταG depends on the concentrations of the molecules in the reaction, whereas for /δ∊λτα G°, the concentrations are set to a fixed value.

A

true

26
Q

For the simple reaction Y → X, the equilibrium constant K is:

A

[X]/[Y]

27
Q

For every 1.42 kcal/mole difference in free energy at 37°C, K changes by a factor of:

A

10

28
Q

Consider the reaction A + B → AB. How is the equilibrium constant expressed for this reaction with two substrates and a single product?

A

K = [AB]/[A][B]

29
Q

Two molecules will bind to each other by means of noncovalent bonds if the /δ∊λτα Γ° of the interaction is:

A

negative (the free energy of the product is lower than the sum of the free energies of the unbound partners).

30
Q

Consider two molecules that associate with each other through hydrogen bonds. The larger the equilibrium constant, K, for this association:

A

the more tightly the two molecules will bind.

31
Q

The overall free-energy change for coupled reactions is equal to the sum of the free-energy changes for each individual reaction.

A

true

32
Q

In cells, small molecules can diffuse over short distances quickly.

A

TRUE

33
Q

The rate at which an enzyme will encounter its substrate depends on:

A

the concentration of the substrate.

34
Q

In an enzyme catalyzed reaction, a low value of KM indicates that a substrate binds:

A

very tightly to the enzyme.

35
Q

When an enzyme lowers the activation energy for the forward reaction X → Y, it also lowers the reaction rate for the reverse reaction Y → X by the same amount.

A

True

36
Q

In isolation, the formation of an activated carrier molecule, such as ATP, NADH, or NADPH, is an energetically unfavorable reaction.

A

TRUE

37
Q

The/δ∊λτα Γ° of the hydrolysis reaction of ATP is -7.3 kcal/mole, but in a cell the actual /δ∊λτα Γ is much more negative because:

A

ATP is much higher in concentration than the products ADP and Pi.

38
Q

Which statement is true about the removal of a terminal phosphate from ATP?

A

The reaction is energetically favorable.

39
Q

Which statement is NOT true about the removal of a terminal phosphate from ATP?

A
  • The reaction is a condensation reaction.

- The reaction is associated with a positive change in /δ∊λτα Γ°.

40
Q

The formation of ATP can be coupled to energetically unfavorable reactions to allow them to proceed.

A

False

41
Q

What is the difference between NAD+ and NADH?

A

NADH carries an extra proton and two high-energy electrons.

42
Q

Which of the following statements is NOT true?

A

NADPH is an activated carrier molecule that is used primarily by plants.

43
Q

Which of the following statements IS true?

A
  • NADPH is an activated carrier molecule that is usually used in biosynthetic reactions to build energy-rich molecules.
  • NADH is an activated carrier molecule that is usually used in oxidation reactions to produce ATP.
44
Q

Which of the following is true?

A

NADPH and NADH are used in independent pathways in cells.

45
Q

Which of the following is NOT true?

A
  • NADPH loses a phosphate group to form NADH during biosynthetic reactions.
  • NADPH and NADH deliver electrons to the same set of enzymes.
  • NADH caries electrons in animal calls and NADPH does the same in plants.
46
Q

Activated carriers that transfer methyl, carboxyl, and glucose groups for the purpose of biosynthesis are typically generated in reactions coupled to ATP hydrolysis.

A

True

47
Q

Which statement is true about the breakdown of polymers?

A

The reaction is associated with a negative change in free energy.

48
Q

Which statement is NOT true about the breakdown of polymers?

A
  • The reaction occurs without the need of enzymes.

- The reaction is energetically unfavorable.

49
Q

What is the difference between catabolism and anabolism? Give an example of each.

A

Catabolic pathways break down foodstuffs into smaller molecules to generate energy for the cell; anabolic pathways use energy to drive the synthesis of the molecules that form the cell. Cellular respiration is an example of catabolism, and photosynthesis is an example of anabolism.

50
Q

Does an enzyme change the Δ G° of the reaction it catalyzes?

A

An enzyme functions by lowering the activation energy of a reaction. At the same time, it lowers the activation energy of the reverse reaction by the same amount. Therefore, the forward and reverse reactions will be accelerated by the same factor. So, the equilibrium point for the reaction, and therefore its Δ G°, will not change.

51
Q

The organic chemistry of living cells is said to be special for two reasons: it occurs in an aqueous environment and it accomplishes some very complex reactions. But do you suppose it is really all that much different from the organic chemistry carried out in the top laboratories in the world? Why or why not?

A

Organic chemistry in laboratories—even the very best—is rarely carried out in a water environment because of low solubility of some components and because water is reactive and usually competes with the intended reaction. The most dramatic difference, however, is the complexity. It is critical in laboratory organic chemistry to use pure components to ensure a high yield of the intended product. By contrast, living cells carry out thousands of different reactions simultaneously with good yield and virtually no interference between reactions. The key, of course, is that cells use enzyme catalysts, which bind substrate molecules in an active site, where they are isolated from the rest of the environment. There the reactivity of individual atoms is manipulated to encourage the correct reaction. It is the ability of enzymes to provide such special environments—miniature reaction chambers—that allows the cell to carry out an enormous number of reactions simultaneously without cross talk between them.